Tacx roller with 20" very slow

We are riding a Tacx galaxia roller with a 20" BMX and we thought it would be fun to hook it up with Zwift for some gaming. But it is very slow compair to the roller speed/pedaling. We have tried different tracks and we got some speed down hill but as soon as it gets flat we just spin and everyone drives by. Here is a video with my sons settings. When he starts to ride he goes up to ha 75% of his max speed on the roller. (I also tried to ride and changed the profil to my weight and age but it is still slow) We use Wahoo cadence and speed sensor.

Video link with all the settings and ride: https://imgur.com/a/FIjE7PX

Hi @Drezen

Welcome to the forum.

This thing is with a BMX you just cant go as fast as a road bike. The BMX just don’t have the gears to keep up with a Road bike.

Lets look at a BMX
The Max wheel speed is 20km/h just spinning in the air.


Now look at a road bike gearing, same RPM
The road bike wheel will spin at 47.9 km/h in the air.


Zwift use the power curve of the trainer to calculate the game speed, so there are some losses due to virtual weight, incline, rolling resistance, drag and many other factors. So you wont see the gear speed calculated above in the game.

So I would say the speed is reasonable.


Thank you for the detailed answer, I think I understand!

But is there not a way to modify it? Kinda like a cheat so it feels more correct.

I actually think it is currently in the right ball park.
When my daughter is on her bike I can run with her but I can’t run with my friends on their road bikes.

Not that I can think of, and I would not even want to go down that road.

You can change the bike gear ratio.

They make nice road bikes for juniors the have bigger gear ratios.


I’m back with related question @Gerrie_Delport_ODZ :slight_smile: Hope everything is good btw

Would it work if I bought a trainer for the BMX. What I read the gears is provided by the resistent of the trainer? If so I would be able to ride the bmx with zwift.

Hi @Drezen

Thing are good thanks.

I think you will have the same problem on the flat roads that the bike gearing just can’t go fast enough to generate enough power on a flat road.


Damn it :sweat_smile: Thank you for the help.